Field of the Invention
This invention relates to a process for dewatering an aqueous dispersion of a clay and transforming the clay solids into pellet form.
Aqueous homogeneous suspensions or colloidal solutions of various kinds of clay minerals can be treated in various ways to reduce the water content thereof, including evaporating the water, filter pressing, flocculating or precipitating the clay solids by the addition of acids or other electro-negatively charged substances, electro-osmosis and centrifugal action. The present invention is related to the flocculation or precipitation process, although it significantly differs therefrom as will be pointed out hereinbelow.
Minerals of the montmorillonite group of clay minerals are so-called expanding 2:1 layer clays. When montmorillonite clays contact water, the water molecules penetrate between the layers of the individual montmorillonite particles. Because of this action and the osmotic swelling that occurs because of double layer repulsion between the layers of individual clay particles, the montmorillonite swells greatly.
The prior procedures for dewatering montmorillonites are generally time-consuming and/or expensive and they do not produce the montmorillonite in the desired form of pellets that are useful for many industrial and commercial applications, such as catalyst carriers, pharmaceutical carriers and absorbents. Additional expensive pelletizing treatments are needed to obtain satisfactory pellets so that the overall expense of obtaining clay pellets is relatively high.
Although a peferred clay material for use in the present invention is montmorillonite or clays which predominantly comprise montmorillonite such as bentonite, in its broader aspects the invention is useful to dewater and pelletize other kinds of clays including illites, kaolinites, chlorites, attapulgites and mixed-layer clays.
It is an object of this invention to provide a process for dewatering aqueous clay dispersions by agglomerating the clay solids and then pelletizing the clay agglomerates so as to obtain clay pellets of relatively large size which are useful for a variety of industrial and commercial purposes.
It is a further object of the invention to provide a process, as aforesaid, which is inexpensive and simple to perform, and which can be performed using conventional, readily available equipment.
The broad process of forming an agglomerated product, such as a pellet or a ball, from a liquid suspension of solid material or materials in a finely divided form has long been known and certain specific processes utilizing the basic concept are set forth in a variety of United States and other patents. Examples of these patents are those to Puddington and Farnand U.S. Pat. No. 3,268,071, Sirianni and Puddington U.S. Pat. No. 3,368,004 and Capes et al U.S. Pat. No. 3,471,267. Briefly, all three of these patents refer to a procedure wherein the powders are suspended in a first liquid which is lyophobic to said powders, a second or bridging liquid is then added thereto which second liquid is chosen or treated so as to be lyophilic to at least certain of said powders and the system is then agitated. This forms the solid material which is lyophilic to the bridging liquid into a plurality of agglomerates whose size and shape depend on the details of said procedure as same are set forth at length in said patents and to which reference is invited. These procedures may be and are used both for the separation of one of a mixture of solids from such mixture and such is the main purpose of the above-mentioned Puddington U.S. Pat. No. 3,268,071, or they may be and are used where the formation of an agglomerated product is the objective itself of the agglomeration procedure and such is the principal purpose of the other two patents above-named.
The invention provides a process for dewatering aqueous dispersions of clays, particularly montmorillonite, and forming pellets of the clay particles contained in such dispersions, which comprises the steps of:
a. adding to the aqueous clay dispersion, (i) hydrophobic organic liquid which is immiscible with water and (ii) liquid conditioner effective to penetrate the clay particles and to displace the interlayer and surface water so that the surfaces of the clay particles become oleophilic, whereby the clay particles are no longer wetted by water but rather are preferentially wetted by the organic liquid and there is formed a two-phase liquid system in which said clay particles are contained essentially only in the organic liquid phase, and the water phase is essentially free of clay particles, PA1 b. agitating the two-phase liquid system to effect repeated collisions of said particles and thereby forming in said system a dispersion in water of agglomerates, said agglomerates consisting essentially of said solid clay particles coated with said hydrophobic organic liquid and having said conditioner adsorbed therein and wherein said agglomerates may contain some water trapped in the interstitial spaces thereof, PA1 c. discontinuing said agitation and separating said agglomerates from the freely drainable water contained in the dispersion obtained in step (b), PA1 d. then drying said agglomerates and removing as much as possible of said hydrophobic liquid, said conditioning agent and trapped water therefrom whereby to obtain substantially dry agglomerates, PA1 e. then dispersing said dry agglomerates and a binding agent for said agglomerates in an additional quantity of said hydrophobic organic liquid to form a suspension of said agglomerates and binding agent therein, PA1 f. adding an aqueous bridging liquid to the suspension of binding agent and agglomerates whereby to displace said hydrophobic organic liquid from the surfaces of said agglomerates and binding agent and to wet said surfaces with said aqueous bridging liquid whereby to form a two-phase liquid system in which said agglomerates and binding agent are contained essentially only in the aqueous bridging liquid phase and said hydrophobic organic liquid is essentially free of agglomerates and binding agent, and agitating the latter two-phase liquid system to effect repeated collisions of said agglomerates and binding agent and thereby forming a dispersion in said hydrophobic organic liquid of pellets, wherein the pellets are coated with water and are impregnated and/or coated with and bound together by said binding agent, PA1 g. discontinuing said agitation and separating the pellets from the freely drainable hydrophobic organic liquid contained in the dispersion obtained in step (f), and PA1 h. then recovering the pellets. Inasmuch as the present invention can make use of well-known equipment, the details of suitable equipment are not disclosed herein. Reference may be made to the three patents noted above, particularly U.S. Pat. Nos. 3,368,004 and 3,471,267, for further details concerning useful equipment and details of agglomeration procedures.